Sound recording and reproducing



Oct. 3, 1944, B A. "PRoc'roR EI'AL SOUND RECORDING AND REPRODUCING 2 Sheets-Sheet 1 Filed March 26, 1942 ATTORNEYS Oct. 3, 1944. B. A. PRO CTOR EFAL 2,359,489

SOUND RECORDING AND REPRODUCING Filed March 26, 1942 2 Sheets-Sheet 2 Oufpuf Level B G v 8 .5 l I 3a a5 INVENTORS'" lnpuf Level BadmAfiwfq/"and fe/d/nandCWT/Z/ede AT TORNEYS Patented Oct. 3, 1944 Barton A. Proctor, Larchmont, and'Ferdinand '0. W. Thiede, Hempst'ead, N. Y.,- assignors to B. A. Proctor Company, Inc., New York, N. Y., a corporation of New York Application March 26. 1942, Serial No. 436,244

.11 Claims.

This invention relates to sound recording and reproducing and more particularly to a machine employing an amplifying device for amplifying electrical currents generated by the sound to be recorded and for applying the amplified currents to a recording unit which is provided with a stylus which forms a sound track in a record corresponding to the original sound. The mechanical features of such a machine in which the sound is recorded on thin, flexible disc records are disclosed and claimed in patent application Serial No. 218,082, filed July 8, 1938, now Patent No.

2,296,870, of which the present application is a continuation in part. In said machine, means for reproducing the recorded sound is'also provided,- such reproducing means comprising a reproducing unit which also has a. stylus engageable with the record. The recording and reproducing units are preferably of the piezo-electric'type, such devices being ideally suited to the purpose because of the powerful drive which may be transmitted to the recording stylus and because of the delicate and accurate responsiveness to the reproducing stylus which may be secured.

When shifting over from recording to reproducing it is highly desirable that only a single amplifying device be utilized for both operations and it is a feature of the present invention that 'a simple switching arrangement is provided whereby the same electron discharge tube amplifier is used for both recording and reproducing.

In the illustrative embodiment of the invention, therecord material is deformed during the recording operation so that it is necessary to supply a substantial amount of energy or power to the recording unit, whereas no deformation of the record material occurs during reproduction so that a lesser amount of energy is adequate for operating the reproducing device or loud speaker. In order to supply such energy in proper amounts, the electron discharge tube amplifier is constructed or a plurality of stages connected in cascade and the switching device is arranged and constructed so that three stages of.

, amplification are used for recording while only two stages are used for reproducing. As disclosed in the aforementionedapplication, the

' switching device is preferably operated. by the same manual control handle or finger piece which shifts the recording and reproducing styluses alternatively into and out of' engagement with the record.

In accordance with a further object of the invention, provision is made in the form of an 'overload protective device for limiting the amplitude (c1. na -100.4)

tively to the input of the-recorder circuit and to the output of the amplifier circuit. A circuit including such a tube has the characteristic that it will absorb no energy from the primary or input circuit with which-it is inductively coupled unless and until the conditions of the primary circuit are such as to induce a potential across the tube in excess of a definite, predetermined value. When such value is exceeded, however, the tube will glow, and the circuit will substantially modify the current flowing in the primary circuit with which the glow tube circuit is coupled and limit the amplitude of the current variations therein.

For a,. better understanding of the invention reference is made to the following description taken in connection with the accompanying drawings in which;

Fig. 1 is a schematic circuit diagram showing the electrical connections between the various parts oi the machine; I

Figs. 2 to 5 show schematic circuit diagrams i1- lustrating diflerent circuit arrangements for lim- I iting the output level of the amplifier to a predetermined value'and,

Fig. 6 shows curves illustrating the manner in which the output level of the amplifier is limited by the action or the glow discharge tube.

The thin flexible disc record 10 is shown as being driven by upper and lower feed rollers ill and i 02 and the stylus I" of the recording unit 30 being in engagement with theupper face of the record, the distance between the stylus and the feed rollers being "exaggerated for the-purpose of clarity. The feed rollers III and I0! are'driven in opposite directions by an electric motor ll through suitable driving connections (not shown) which are shown and fully described in the aforementioned application. The driving motor I. may be connected to the alternating current supply mains Mthrough the on ofl" switch ill, the mains M also supplying the current to themplifier tubes 33!, 336 and Illand the rectifier 30 I .7 The rectifier 3M supplies unidirectional current to the circuits of the amplifier tubes through a filter circuit or known type comprising the inductors 303 and condensers 304. The current corresponding to the sound to be amplified is applied across the end of primary winding 3" of transformer 306 whose secondary winding I is connected across the grid and cathode of tube 3", as shown. Resistance coupling is used to manual volume control permitting the user to operate the device at any desired volume level so as to secure optimum results in either recording 1 or reproducing. Resistor 3l5 and condenser 313 transfer the amplified current to the grid circuit of tube 331, the current corresponding to the amplified sound or signal passing through primary winding 3|8 of the output transformer 311.

As shown, transformer 3 l1 preferably has three secondary windings 3l3, 323 and 322, winding 323 being connected through ressitors 32l to the two electrodes of a neon tube 323 which'iunctions as an automatic volume control device, as will be described later.

recording unit 333 through a resistor 343 and its other end to a switch contact 342 engageable by a switch blade 321 carried by a switch control shaft 324. The ends of secondary winding 3" are connected to a pair of switch contacts 3 adapted to be engaged by the switch blades 325 also operated by the shaft 324. The switch blades 325 connect to the terminals of a jack 323 in which may be inserted the Jack plugs 33I or 332. Jack plug 33| 'isshown connected to the ends of a telephone search coil 333 and plug 332 to a unit 334 functioning as either a loud speaker or a microphone transmitter. The reproducer unit 23 has its high potential terminal connected to a. switch contact 344 engageable by a switch blade 323 also connected to shaft 324., switch blade 328 serving to complete the circuit across transmission line 3 I 2 in the position shown.

With the switches in the position shown, the sound received by the microphone 334 may be recorded by inserting plug 332- in jack 323 after closing switch 332 to start the motor 43. Ourrent corresponding to the sound waves passes through primary winding 331, is amplifiedfby' ator should, therefore, lower the volume control best results in recording. If, on the other hand,

the volume contro1 3 was initially set too low, it should be raised to a point where the neon tube commences to glow faintly and left at that setting until the recording is completed.

To record a message passing over. a telephone line the plug 33| is inserted in jack 326 and the Qne end of secondary winding 322 is connected to one terminal of the 1 search coil 333 placed close to the line and inductively coupled therewith as closely as-possible. The currents induced in the search coilare then amplified and recorded in the manner abbve described.

To produce the sound recorded on a record, a handle (not shown) is moved to the reproduce position which causes the reproducer stylus to engage the record and also rotates shaft 324 clockwise by means of connections shown in the aforementioned application, thereby disconnecting recorder 33. Engagement of contact 344 by switch arm 323 causes the outputvoltage of 23 to be impressed on the grid of tube 335. The voltage is amplified'in tubes 333 and 331 and is transferred to switch terminals 3 by primary 3l8 and secondary winding 3l3. Switch arms 325 being now in engagement with these terminals, the sound, as reproduced, may be heard from speaker-334 whose plug 332 is in position in jack 326. It thus appears that the switching arrangetubes 335, 333 and 331 and transferred to recorder 33 through secondary winding 322 of the output transformer and switch blade 321. This causes the stylus of the recorder to move back and ment is such that three stages of amplification are used for recording the signal, whereas for its reproduction only two stages of amplification are used. The switching arrangement disclosed thus effects the proper circuit connections with the amplifier to secure the desired degree of amplification.

Fig. 2 shows an alternative arrangement for connecting the glow tube 323, the recorder 33 and the loud speaker terminals 3 to the output circuit of the amplifier 331. In this case instead of the secondary windings M3, 323 and 322 being directly inductively coupled .to the primary winding 3l3 as in'Fig. 1, they are indirectly coupled thereto by means of a closed link circuit 345, as

, shown.

forth sidewise andform a groove in the record which corresponds to the sound waves. Informing the groove, the stylus merely displaces the material of the record; that is, the material is not removed from the record as when a cutting action is used. We have found when a glow tube,

such as one containing neon or argon gas, is connected as shown, if the microphone is subjected to very loud sounds, the gas in the tube breaks down or glows and causes a, substantial decrease in the voltage applied to the recorder. The sounds In the arrangement shown in Fig. 3, only two secondary windings are provided in the transformer 3", both the-glow discharge'tube 323 and the recorder 33 being connected in parallel across the ends of the secondary winding 323 when the switch 321 is in the recording position shown. I

In'the arrangement of Fig. 4, the coil 3l8,

which is in theplate circuit of amplifier tube of low and medium or normal intensity, however, do not produce sufficient voltage to cause tube V 323 to glow'so that the fully amplified voltage corresponding thereto is impressed on secondarywinding 322 and the recorder.

The glow tube thus serves to limit the energy applied to the recorder from a sound of excessive intensity,

whereas that corresponding to a sound of low or normal intensity is not limited but applied with full effect;

Withthe glow tube disposed within sight of the operator, it thus acts as an indicator, the intense glowing of the tube indicating that the output .voltage of the amplifier is too high. The oper- I3 331; not only serves as a primary winding for v the secondary winding 3|! which supplies current to the loud speaker 334', but also forms part of a step up auto-transformer 343. The amplified signal voltage is supplied to both the glow discharge tube 323 and the recorder 33, which are connected in parallel, through the circult shown. This circuit includes a blocking condenser 341, one side of which is connected I to the high potential terminal of the auto-transformer 346. A single resistor 348 is shown connectedin series with the glow discha ge tube for limiting the current therethrough.

The invention also has utility where the amplified signal is not to be recorded but is used merely to operate a loud speaker having ahigh sound output capacity. Such an embodiment is shown in Fig. 5, in which the secondary winding 313 is connected to the movable Voice coil 8 of, the

electrodynamic loud speaker 334'. By using a neon tube 323 of suitable size as the signal voltage applied to the grid of the amplifier tube 331 is increased to a value at which the neon tube commences to glow, the tube acts as a bleeder resistor and as the energy in the'output circuit of the amplifier is further increased, a greater proportion of it is consumed in lighting the neon tube. The result is that for signals above a certain level, the voltage applied to the secondary winding 3I9 remains substantially constant at a value at which the loud speaker 334 operates satisfactorily and is not overloaded. For weak signals, the amplified signal current in the primary winding SIB is insufiicient to cause the neon tube 323 to glow so that the tube has substantially no efiect on the current in the primary winding. Weak signals are therefore reproduced at their proper levels by the loud speaker 334'.

In all of the illustrated embodiments of the invention, the amount of energy loss to be introduced into the controlled circuit or the level at which the glowvtube is to become efiective may be controlled by the use of glow tubes of diiTerent sizes or by the use of resistors of different values in series with the glow tube.

Fig. 6 illustrates the action of the glow tube in limiting the output level of the amplifier and the voltage applied tothe recorder. The full line A represents the output level of the amplifier for difierent levels of signal voltage applied to its grid when the glow tube is not used. It will be noted that the line is straight and that the output' level and the voltage applied to the recorder are proportional to the input level of the amplifier, the point C indicating the maximum output of the amplifier.

The dotted curve D represents the output level of the amplifier when the neon control tube is used. It will be noted that for signal levels up to 15, the two curxes practically coincide showing that for low signal levels the neon tube has substantially no efiect on the amplifier. At

a level of approximately 15 the tube starts to glow, however, and it will be noted that as the signal level is increased above 15, the spacing between the curves C-D progressively increases, indicating that a larger proportion of the available energy is consumed in lighting the neon tube. By designing the neon tube of the proper size, the maximum output level and the voltage applied to the reproducer or loud speaker may be limited to any desired value.

We have described what we believe to be the best embodiments of our invention. We do not wish, however, to be confined to the embodiments shown, but what we desire to cover by Letters Patent is set claims.

We claim:

1. In a sound translating device, the combination of at least three coupled amplifier stages.

- connectingsaid reproducing device to the input circuit of the second stage for reproducing, circuit means including switch mechanism for connecting the combined microphone and speaker alternatively to the input circuit of the first forth in the appendedthe third stage for reproducin and a single control means for said switches and switchmechanisms to cause the switch over from recording to reproducing and the switch over from reproducing to recording each to'be completely efiected instantaneously and at a single operation.

.2. In a sound translating device, the combination of an electron discharge amplifier device having input and output circuits, a source of currents of audio frequency connected to said input circuit, a record, means for rotating said record, a recording device having a stylus in engagement with said record, a circuit coupling said recording device to said output circuit, and

a glow discharge tube coupled to said output circuit and arranged to glow when the current variations in said output circuit exceed a pregaging said record, a circuit coupling said recstage'forrecording and to the output circuit of ording device to said output circuit, a coil inductively coupled to said output circuit, a neon tube having two spaced apart electrodes, and circuit connections between said electrodes and the ends of said coil, said neon tube being constructed to glow only in response to the impression on its electrodes of a voltage above a predetermined value.

4. In a sound translating device, the combination of an electron discharge amplifier having an input circuit and an output circuit including a transformer having at least three secondary windings, a. glow discharge device connected.

across one of said windings, a recording device, a circuit including a first switch arranged to connect said recording device to a second one of said windings, a sound translating device, a circuit including a second switch arranged to connect said translating device to the third of said windings and means for opening said first switch and closing said second switch substantially simultaneously.

5. In a sound translating device, the combination of an amplifying device having a plurality of stages connected in cascade, an acoustic translating device, a recording device, a reproducing device, electrical circuit connection comprising a plurality of movable switch blades arranged to selectively connect said reproducing device to the input of one of said amplifying stages other than the first and said acoustic device to the output of the last amplifying stage whereby the acoustic device generates the reproduced soundwaves; or to connect said recording device to the output circuit of the last amplifying stage and said pletely efi'ected instantaneously and at a single operation.

6. In a sound translating device, the combination of an amplifying device having a plurality of stages connected in cascade, an acoustic translating device, a recording device, a reproducing device, and electrical circuit connections comprising a plurality of movable switch blades arranged to selectively connect said reproducing device to the input of one of said amplifying stages other than the first and said acoustic,

device to the output of the last amplifying stage whereby the acoustic device generates the re-' produced sound waves; or to connect said recording device to the output circuit of the last amplifying stage and said acoustic device to the cascade, a source of currents of audio frequency connected to the input of the first stage, a

record, means for rotating the record, a recording device having a stylus in engagement with the record, a circuit coupling said recording device to the output of the last amplifying stage, a

glow discharge tube coupled to the output of the last amplifying stage, and an adjustable volume ccntrcji device connected to one of the amplifying stages and adapted to increase the amplitude of the current in the last stage to a level at which the said discharge tube commences to glow faintly.

8. In a sound translating device, in combination, an electron discharge tube amplifier device having a plurality of stages connected together in cascade, a source of currents ,of audio frequency connected to the input of the first stage, a record, means for rotating the record, a recording device having a stylus in engagement with the record, a glow discharge tube having a pair of spaced electrodes, acircuit connecting the terminals of the recording device and the electrodes of the glow tube in parallel and means coupling said circuit to the output of the last amplifying stage, said glow tube being arranged to glow in response to an increase in the output current of the last stage to a predetermined value. 9. A sound translating device as claimed in claim 8 in which the coupling-means comprises an auto-transformer having a coil disposed in the output circuit of the last amplifying stage.

10. A sound translating device as claimed in claim 8 in which the coupling means comprises an auto-transformer having a coil disposed in the output circuit of the last amplifying stage and a, condenser having one side thereof connected to the high potential point on said trans former coil.

' 11. In a sound translating device, in combination, an electron discharge tube amplifier device having a plurality of stages connected together in cascade, a source of currents of audio frequency connected to the input of the first stage, an electro-dynamic loud speaker having its voice coil coupled to the output of the last stage and control means comprising a glow discharge tube having at least two spaced apart electrodes coupled to the output of the last stage, said discharge tube being arranged to glow and limit the current in the voice coil to a desired value in response to an increase in the output current of the last stage to a predetermined value.

BARTON. A. PROCTOR. FERDINAND C. W. I'I-IIEDE. 

